The present invention relates to turbine-generator installations, and is particularly concerned with installations in which steam for driving a series of turbines is produced by a nuclear reactor and is subject to reheating during delivery between turbines.
Among the electrical power plants utilized by the electric power industry, there are nuclear plants in which steam derived, for example, from a boiling water reactor or a pressurized water reactor is conducted through a series of steam turbines all connected to a common output shaft which drives a generator. In certain installations of this type, the steam is conducted first through a high pressure turbine, the steam leaving that turbine is subjected to moisture separation and reheated. The reheated steam is supplied to a plurality of low pressure turbines. The steam flows in parallel paths through the low pressure turbines.
The basic steam flow path of such an installation is illustrated in FIG. 1. Steam is produced by a reactor 2, which may be a boiling water reactor or a pressurized water reactor, and this steam is delivered via a supply path 4 to the steam inlet of a high pressure turbine 6. The steam leaving the steam exhaust of turbine 6 is then passed through a moisture separator-steam reheater (MSR) assembly 8 in which it is reheated by indirect heat exchange with steam derived from supply path 4, the reheated steam being delivered to the steam inlets of two low pressure turbines 10 and 12.
The exhaust from turbines 10 and 12 is conducted back to a feed water heating assembly 14 in which feed water is heated to an appropriate temperature for reintroduction into reactor 2. The heating steam delivered from path 4 to assembly 8 is also conducted, after passing through assembly 8, to feed water heater 14.
While assembly 8 is illustrated essentially as a heat exchanger, it is, according to the prior art, also provided with components for extracting moisture from the exhaust steam from turbine 6.
The physical layout of the turbines and moisture separator-reheater assemblies of a typical prior art installation is illustrated in plan view in FIG. 2. Since the physical size of a moisture separator-steam reheater device must be limited to certain dimensions primarily to satisfy existing shipping requirements, the moisture separation and reheating of the requisite quantity of steam requires the provision of two moisture separator-reheater assembly units 8. Preferably, as shown in FIG. 2, units 8 are disposed at respectively opposite sides of turbines 6, 10 and 12, so that they can be located to be serviced from the turbine deck, which is a floor on which the turbines are also supported. Appropriate piping is provided to deliver high pressure steam from supply path 4 to the steam inlet of high pressure turbine 6, and from the exhaust outlets of turbine 6 to each of units 8. Exhaust steam from high pressure turbine 6 is delivered to moisture separator-reheater assemblies 8 via conduits 16, which lead to the bottom of assemblies 8, while reheated steam is delivered to the steam inlets of low-pressure turbines 10 and 12 via conduits 18 which emerge from the top of assemblies 8. According to conventional practice, conduits 18 extend in directions normal to the axis of the turbine shaft.
In many installations, it is necessary to effect deareation of the steam and, with the layout illustrated in FIG. 2, there is no room for locating a deareator at level of the turbine deck. This means that the deareator must be located at a different level, which increases servicing problems.
Moreover, the component layouts currently in use, an example of which is shown in FIG. 2, are disadvantageous in that they limit access to turbines 10 and 12, reduce the amount of working space available on the turbine floor during routine maintenance operations, and will result in uneven thermal loading of turbines 10 and 12 if one of assemblies 8 must be removed from service during plant operation.
In certain known installations typified by FIG. 2, the reheater components of each assembly are composed of a plurality of U-shaped tubes which conduct reheating steam and which are oriented to each lie in a vertical plane. This orientation gives rise to drainage problems in the lower leg of each tube, requiring the provision of additional components in the assembly. By way of example, it is known to provide a scavenging steam vent condenser which converts what is in reality a two-pass bundle into a modified four-pass arrangement, thereby increasing scavenging steam flow in the lower legs of the U-shaped tubes.